Under the hood
Side-query API requests now retry once without the side-query header on certain failures.
Outgoing beta.messages.create API dispatch requests may now attach a header identifying the query as a "side query." If such a request fails with a 5xx error, a connection error, or a 408/409/429 with retries remaining, it is retried once without the header or the maxRetries override, and telemetry is emitted for the fallback.